Communications interfaces using multiple wire connections are well represented in the art. Historically, parallel wire cables were supplanted by twisted pair and shielded cables at low frequencies and stripline and microstrip transmission lines at higher frequencies, in an effort to minimize electro-magnetic interference (EMI) emission. Vector signaling is a method of signaling. With vector signaling, pluralities of signals on a plurality of wires are considered collectively, although each of the plurality of signals may be independent. One encoded unit of the vector signaling code is termed a “codeword”, and each of the collective signals of a codeword is referred to as a component, with the number of signals communicated on the plurality of wires representing one codeword referred to as the “dimension” of the vector.
With binary vector signaling, each component takes on a coordinate value (or “coordinate”, for short) that is one of two possible values. As an example, eight single ended signaling wires may be considered collectively, with each component/wire taking on one of two values each signal period. A “code word” of this binary vector signaling is one of the possible states of that collective set of components/wires. A “vector signaling code” or “vector signaling vector set” is the collection of valid possible code words for a given vector signaling encoding scheme. A “binary vector signaling code” refers to a mapping and/or set of rules to map information bits to binary vectors.
With non-binary vector signaling, each component has a coordinate value that is a selection from a set of more than two possible values. A “non-binary vector signaling code” refers to a mapping and/or set of rules to map information bits to non-binary vectors. The ability of a vector signaling code to encode data is constrained by the number of codewords in the code, with larger codeword sets being capable of encoding more data. The ratio of encoded data capacity (i.e., the binary logarithm of the number of codewords) to the dimension of the codewords (or equivalently, to the number of actual bits transmitted via the codeword versus the number of physical pins or wires needed to communicate that number of bits in parallel,) is known as the pin-efficiency of the vector signaling code. Examples of vector signaling methods are described in Cronie I, Cronie II, and Fox I.
Viewed as a layered networking model, significant effort has been expended at the physical layer to optimize wiring, transmission line characteristics, signal amplitudes, etc. to minimize undesirable signal emission. An analysis of signal coding methods indicates that significant EMI reduction may be obtained by careful selection of appropriate signal encodings, such as particular vector signaling codes, for signals transmitted over such physical media.